Often, in applications involving microwave/RF circuitry, it is necessary to tune the electrical characteristics of certain parts of the circuitry after it has been manufactured. Actually, with high-performance devices, such as high-Q microwave/RF resonators and several-pole microwave/RF filters, continual fine tuning often is required even after the initial tuning. Currently, both the initial tuning, and the subsequent fine tuning are achieved almost exclusively by mechanical means such as tuning screws, or by adding or removing wire-bonding from tuning pads placed on critical parts of the circuitry. This mechanical tuning is time consuming, and is found to be lacking in the area of controllability, accuracy and resolution.
Bulk ferrite materials also have been utilized for magnetically tunable microwave devices whose response can be tuned by applying a dc magnetic field. However, tunable and adaptive devices incorporating ferrites so far have had limited use due to their high unit cost, complexity, large size, high insertion loss, and low tuning speed.
The invention disclosed herein is related loosely to two previous issued to the inventor herein. These patents are: U.S. Pat. No. 5,538,941, issued Jul. 26, 1996, for SUPERCONDUCTOR/INSULATOR METAL OXIDE HETEROSTRUCTURE FOR ELECTRICALLY TUNABLE MICROWAVE DEVICES; and U.S. Pat. No. 5,604,375, issued Feb. 18, 1997, for SUPERCONDUCTING ACTIVE LUMPED COMPONENT FOR MICROWAVE DEVICE APPLICATION.
If possible, a way of tuning circuitry electrically which could be implemented in conventional planar microwave and RF circuitry with minimal modification in design and with negligible pertubation of device performance would be far superior to the conventional tuning regimes of the prior art. Tuning circuitry electrically also could provide a convenient means for adding adaptive features to the operation of the tuned device.
Electrical tuning of microwave/RF circuitry does provide many advantages over both mechanical and magnetic tuning. Among these advantages are convenience, reproducibility, controllability, versatility, speed, accuracy, resolution and adaptability. The method according to the present invention uses electric field induced changes in the permittivity of certain nonlinear dielectric thin film under specific bias configurations to effect electrical fine tuning of microwave/RF circuitry. The broad class of materials known as nonlinear dielectrics possess many characteristics which make them suitable for this application. Among these characteristics are high peak power capacity, short switching times, broadband capability, and easy integration into monolithic microwave/RF devices.
It is therefore an object of the present invention to provide apparatus and method for the localized electrical fine tuning of passive microwave and RF devices through local manipulation of the shunt and series capacitance of the devices.
It is another object of the present invention to provide apparatus and a general-purpose method for localized electrical fine tuning of conventional passive microwave and RF devices which provides improved speed, reproducibility and accuracy, without significant degradation of device performance.
It is yet another object of the present invention to provide apparatus and method for localized electrical fine tuning of conventional passive microwave and RF devices that can be incorporated into the devices either at the time of manufacture or after manufacture of the devices.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the combinations particularly pointed out in the appended claims.